It is generally known that the depth of field narrows down with an increase in the number of pixels of an imaging element in a device including the imaging element such as an endoscope system. More specifically, if the pixel pitch (horizontal and vertical dimension of one pixel) is reduced to increase the number of pixels in the imaging element, the permissible circle of confusion is also reduced accordingly, and the depth of field of the imaging apparatus narrows down. To expand the depth of field, for example, Patent Literature 1 is disclosed, wherein an optical path division means divides a subject image into two images with different focuses. Different imaging elements form the images, and the two images are combined to acquire an image with an expanded depth of field.
On the other hand, an aperture value of an optical system can be increased to maintain the depth of field. However, there are problems that the image quality is degraded by an increase in noise and that the resolving power is decreased by an increase in the influence of diffraction. An example of a technique for improving the resolving power is disclosed in Patent Literature 2, wherein one imaging element forms two subject images with different focuses divided by an optical path division element, and the two images are added to acquire a combined image with improved resolving power.